What is the meaning of territorial sea?

(DoD) A belt of ocean space adjacent to and measured from the coastal state's baseline to a maximum width of 12 nm. Throughout the vertical and horizontal planes of the territorial sea, the coastal state exercises sovereign jurisdiction, subject to the right of innocent passage of vessels on the surface and the right of transit passage in, under, and over international straits. Territorial sea areas that are a continuation of sea lanes through archipelagoes are subject to archipelagic sealane passage, with the same transit rights as those that apply to international straits.